China wants a clear explanation from Washington over a report that the U.S. National Security Agency infiltrated servers at the headquarters of telecoms giant Huawei Technologies Co., a Chinese foreign ministry spokesman said on Monday.

Hong Lei, the spokesman, said China was "extremely concerned" about the spying allegations.

"Recently, the international media has put out a lot of reports about the eavesdropping, surveillance and stealing of secrets by the United States of other countries, including China," he told a regular briefing.

"China has already lodged many complaints with the United States about this. We demand that the United States makes a clear explanation and stop such acts."

The New York Times and German magazine Der Spiegel on Saturday reported on classified documents, provided by former agency contractor Edward Snowden, that detailed the spying operation.

Der Spiegel also reported that the NSA was targeting China's political leadership, including former President Hu Jintao, as well as the trade and foreign ministries.

Questions over cyber-espionage have cast a shadow over China-U.S. ties, with each side accusing the other of spying.